Electric motor with redundant electric circuits

ABSTRACT

An electric motor having a stator defining a number N, at least equal to two, of pairs of poles and a rotor mounted to pivot in the stator. The motor has a number n of electric circuits each defining two windings mounted on poles of the stator, the windings of all the circuits being substantially identical to each other, the number n of electric circuits being greater than the number N of pairs of poles and at least first and second electric circuits being mounted on a first of the pairs of poles and a third of the electric circuits being mounted on a second of the pairs of poles.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric motor, more particularly asingle-phase motor.

2. Brief Discussion of the Related Art

Such single-phase motors are for example used for moving flying surfacesin an aircraft equipped with electric flight controls.

Such electric motor comprises a stator defining a number at least equalto two, of pairs of poles and a rotor mounted to pivot in the stator.The motor comprises an electric circuit defining identical windingsmounted on the poles of the stator so as to form the motor phases. Themotor may be so arranged as to require a limited motion space. Thedesired motion space for the motor determines the number of pairs ofpoles: if one pair of poles is enough for a 180° maximum motion space,two pairs of poles are required for a 90° maximum motion space and threepairs of poles are required for a 60° maximum motion space.

For safety reasons, and more particularly in aeronautic applications,linking two motors equipped with their own motion transmission meanswith the same flying surface, with both motors being so dimensioned asto be able to move the flying surface alone is known. In case of failureof one motor, the other motor can thus move the flying surface. Suchsolution is relatively heavy and cumbersome.

Using an actuator with two or even three motors sharing the same outputshaft has also been considered. Three stators are then mounted along theshaft, each one being positioned opposite one segment of the shaft whichis so arranged as to form a rotor. Such solution is less heavy and lesscumbersome while meeting the same safety requirements as the previoussolution.

BRIEF SUMMARY OF THE INVENTION

The invention aims at providing a motor complying with the same safetyrequirements in case of failure, while being less heavy and lesscumbersome.

For this purpose, the invention provides for an electric motorcomprising a stator defining a number N, at least equal to two, of pairsof poles and a rotor mounted to pivot in the stator. The motor comprisesa number n of electric circuits each defining two windings mounted onpoles of the stator and the windings of all the circuits aresubstantially identical to each other. The number n of electric circuitsis greater than the number N of pairs of poles. At least a first one anda second one of the electric circuits are mounted on a first one of thepairs of poles and a third one of the electric circuits is mounted on asecond one of the pairs of poles.

The motor of the invention thus comprises several electric circuitsenabling the control of the motor so that the failure of one of thecircuits does not prevent the motor from operating. The motorarrangement thus enables a redundancy of the electric circuits even formotors including a relatively low number of poles. This is particularlyinteresting for motors having a limited motion space.

According to a first embodiment of the invention, the windings of eachone of the first and second electric circuits are mounted on differentpoles of the first pair of poles.

If the first or the second electric circuit fails, the motor can thusstill be provided with the same torque, provided the feed current of theremaining electric circuit is increased.

According to one second embodiment of the invention, the windings ofeach one of the first and second electric circuits are mounted on thesame pole of the first pair of poles.

Such embodiment is simpler than the first one. On the contrary, if thefirst or the second electric circuit fails, the motor can be providedwith only half the maximum torque that could be supplied by the motorwhen both electric circuits are operational.

According to an advantageous embodiment of the stator:

-   -   each pole is formed with a tooth having an enlarged free end.    -   the stator is formed of angular sectors which each include one        of the poles and which are assembled together.

The winding can thus be provided on each sector prior to the assemblingtogether of the sectors, which makes the production of the statorsimpler.

The number N of pairs of poles is then preferably equal to two and thestator has a cross-section with a square-shaped outer profile.

The square shape is advantageous since it leaves a relativelysignificant space for the windings.

Other characteristics and advantages of the invention will becomeapparent upon reading the following description of particularnon-restrictive embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is made to the appended drawings, wherein:

FIG. 1 is a schematic half-view in perspective of a motor according to afirst embodiment of the invention;

FIG. 2 is a cross-sectional schematic view along plane II of FIG. 1 ofthe motor according to the first embodiment of the invention;

FIG. 3 is a cross-sectional schematic view of a stator according to analternative embodiment; and

FIG. 4 is a view similar to FIG. 2 of a motor according to a secondembodiment of the invention.

DETAILED DISCUSSION OF THE PREFERRED EMBODIMENTS

The invention is described here relative to a single-phase electricmotor having a limited motion space, for instance 70°.

Referring to FIGS. 1 to 3, the electric motor comprises a stator 1 and arotor 2 so mounted as to pivot in the stator 1 about an A axis. Therotor 2 is known per se and, as the invention does not relate thereto,it shall not be described in greater details hereafter.

The stator 1 has two pairs of teeth 3 symmetrically opposite each otherto define two pairs of poles. The teeth 3 of one pair extend at 90°relative to the teeth 3 of the other pair. Each tooth has an enlargedfree end which extends semi-circularly around a portion of the rotor 1.

The body of the stator 1 knowingly comprises sheet panels placed side byside along the A axis. The body of the stator 1 here has a sectiontransverse to the A axis, with a square-shaped outer profile.

The body of the stator 1 is formed with angular sectors which eachcomprise one of the teeth 3 and which are assembled together by a fingerjoint. The finger pitch shall preferably be one or two panel(s). Thefinger joint makes it possible to increase the covering surface and tomake the motor less sensitive to stray gaps.

As the motor comprises three electric circuits generally referred to as10, each defining two windings 11, 12 in series (the electric circuitsand the windings thereof are differentiated by the numbers 1, 2 and 3which appear after the reference 10, 11, 12 respectively). The windings11, 12 each enclose one of the teeth 3 and are substantially identical.A first one and a second one of the electric circuits 10, respectivelybearing references 10.1, 10.2, are mounted on one of the two pairs ofteeth 3 and a third one of the electric circuits, bearing reference 10.3is mounted on the other one of the pairs of teeth 3.

The winding 11.1 of the first electric circuit 10.1 and the winding 11.2of the second electric circuit 10.2 enclose one of the teeth 3 of thepair of teeth 3 and the winding 12.1 of the first electric circuit 10.1and the winding 12.2 of the second electric circuit 10.2 enclose theother one of teeth 3 of the same pair of teeth 3. The windings 11 and 12of each one of the first and second electric circuits 10.1, 10.2 arethus mounted on different poles of the first pair of poles.

The winding 11.3 and the winding 12.3 of the third electric circuit 10.3each enclose one of the teeth 3 of the other pair of teeth 3.

The windings are wound about the teeth 3 prior to assembling the sectorsto build the stator 1. The windings are each formed with an electricallyconductive wire wrapped in an insulator and the windings of the sametooth are separated from each other by the insulator and separated fromthe stator by an insulator too. The insulator may consist of an annularsupport having a C-shaped cross-section defining a peripheral recesswhich accommodates the winding.

It should be noted that the windings 11, 12 have portions extending inan axial protrusion from the body of the stator 1. Said protrudingportions are covered with a cap 15 (only two of which are shown in FIG.1). The caps 15, made of a magnetic material, are so arranged as tocanalise the leakage flux. This facilitates the filtering of highfrequency currents generated by the decoupling control of the motor andthe insulating of the windings from one another relative to such highfrequency currents.

In the alternative embodiment shown in FIG. 4, the stator 1 is made oftwo parts, i.e. a tubular inner body 1.1 including teeth 3 whichprotrude outwards and a tubular engine head 1.2 enclosing the tubularinner body 1.1.

The elements identical with or similar to those described above aregiven the same reference numbers in the following description of thesecond embodiment of the invention.

The motor in FIG. 5 is identical with that of the first embodimentexcept for the windings 11, 12 of each one of the first and secondelectric circuits 10.1, 10.2, which are mounted on the same pole of thefirst pair of poles.

More precisely, the windings 11.1, 12.1 of the first electric circuit10.1 enclose one of the teeth 3 of one of the two pairs of teeth and thewindings 11.2, 12.2 of the second electric circuit 10.2 enclose theother one of the teeth 3 of the same pair of teeth 3.

As mentioned above, the winding 11.3 and the winding 12.3 of the thirdelectric circuit 10.3 each enclose one of the teeth 3 of the other pairof teeth 3.

Of course, the invention is not limited to the described embodiments butencompasses any alternative solution within the scope of the inventionas defined in the claims.

More particularly, the number n of electric circuits and the number N ofpairs of poles may be different from three and two.

The motor may not include any cap.

The stator may include decoupling portions extending between thewindings of adjacent teeth.

The stator may have different shapes and for instance a circular outershape.

1. An electric motor comprising a stator defining a number N, at leastequal to two, of pairs of poles and a rotor mounted to pivot in thestator, with the motor comprising a number n of electric circuits, eachdefining two windings mounted on poles of the stator, with the windingsof all the circuits being substantially identical to each other, withthe number n of electric circuits being greater than the number N ofpairs of poles and with at least first and second electric circuitsbeing mounted on a first one of the pairs of poles and a third one ofthe electric circuits being mounted on a second one of the pairs ofpoles.
 2. The motor according to claim 1, wherein the windings of eachone of the first and second electric circuits are mounted on differentpoles of the first pair of poles.
 3. The motor according to claim 1,wherein the windings of each one of the first and second electriccircuits are mounted on the same pole of the first pair of poles.
 4. Themotor according to claim 1, wherein each pole is formed with a toothhaving an enlarged free end.
 5. The motor according to claim 4, whereinthe stator is formed of angular sectors which each include one of thepoles and which are assembled together.
 6. The motor according to claim5, wherein the angular sectors are linked by a finger joint.
 7. Themotor according to claim 4, wherein the number N of pairs of poles isequal to two and the stator has a cross-section with a square-shapedouter profile.
 8. The motor according to claim 4, wherein the stator ismade of two parts, i.e. a tubular inner part including the poles and atubular engine head enclosing the inner part.
 9. The motor according toclaim 1, wherein the windings have portions extending in an axialprotrusion of the stator and the protruding portions are covered with acap made of a magnetic material in order to canalise the leakage flux.